1. Field
The present invention relates to the field of water conservation as applied to residential hot water plumbing of the non-circulating storage tank heater type.
2. State of the Art
Virtually all household hot water systems used in the United States use a central storage-tank type water heater. Each such heater comprises a device for applying heat energy to water, and an insulated storage tank for the heated water. Typically households are equipped with a single storage tank heater, having a capacity of from 15 to 60 gallons, from which hot water is piped to the various locations at which it may be used.
When hot water is not being drawn from a central storage-tank type water heater, the pipes, with the water in them, leading from the heater will cool to the temperature of the surrounding environment, the ambient temperature. When a consumer opens a hot water tap, water is received at the ambient temperature. Hot water of the desired temperature only reaches the tap after the cooled water is removed from the pipes, and enough hot water has flowed through the pipes to warm the pipes.
The initial water drawn from the hot water tap, the cool water at ambient temperature, is often wasted. Waste often occurs when typical consumers take showers. A consumer will turn on the hot water tap, allowing the water received to run down the drain. When the water at ambient temperature is purged from the pipes, and hot water reaches the tap, the consumer will adjust the temperature and enter the shower. Other consumers may turn on the hot water, allowing water to flow down the drain, while performing some unrelated task. Sometime later, after hot water has reached the tap, the consumer will return to the shower, adjust the temperature, and begin the shower. This not only wastes water, but increases the load on the sewage system being used because of the increase in volume of liquid sewage to be treated.
Experiments at the inventor's residence showed that about 4.3% of the inventor's domestic water consumption for a family of two people, or about 4.5 gallons per day, may be wasted in this manner. A larger family will have greater waste. It is therefore advantageous if the loss of some of this water can be prevented.
The amount of water wasted while purging hot water pipes can be reduced through use of a demand-type water heater located close to the tap. Multiple demand-type water heaters are often required if water wastage is to be eliminated because the various taps are not always located close to each other. Further, demand-type water heaters are usually electric water heaters and are significantly less efficient than natural gas fired heaters of the storage tank type.
Another method for reducing the amount of water wasted while purging pipes is the continuously circulating hot water system. With this system, the pipes leading from the hot water heater are arranged in a loop, passing near each tap, with a return pipe to the hot water heater. A pump is inserted in the loop to keep hot water flowing through the loop, thereby keeping the pipes and the water in them at a high temperature. This system is less energy efficient than the typical system because of the heat radiation from the pipes, and is difficult to retrofit to existing buildings. This system is nonetheless common in large buildings with many bathrooms such as hospitals.
U.S. Pat. No. 5,277,219, issued to Lund on Jan. 11, 1994, shows a water saving hot water system wherein an electric pump is used to pump ambient temperature, cool water from the hot water pipe into the cold water pipe. A switch is pressed to turn on the pump when hot water is desired. The pump turns off when a temperature sensor detects that the cool water has been purged from the hot water pipe. A similar system is portrayed in U.S. Pat. No. 5,105,846, issued to Britt on Apr. 21, 1992, in which a timer shuts off the electric pump. Yet another such system is portrayed by U.S. Pat. No. 5,009,572, issued to Imhoff on Apr. 23, 1991. Since the typical residential hot water system is fed from the same potable water source as the cold water system and the hot and cold water is typically at approximately the same static pressure, pumping the cool water from the hot water pipe into the cold water pipe is a reasonable way to conserve this cool water. However, systems using electrical pumps require electrical power to operate the pumps which offsets any savings realized due to saving water. Further, such systems are somewhat complex to install, maintain, and operate.